Oligosaccharides are molecules containing complex sugars. Cell surface oligosaccharides play critical roles in their clearance of serum glycoproteins, in targeting lysosomal enzymes and in mediating adherence of bacterial pathogens to epithelial cell surfaces. Recently, specific alpha(1,3) and alpha(1,4) fucosylated oligosaccharide molecules have been shown to mediate the adhesion of immune cells to vascular endothelia, via selectin molecules endothelium. Additionally, these fucosylated oligosaccharides may have important roles in embryogenesis. The biosynthesis of these determinants is dependent on an alpha(1,3)fucosyltransferases (a(1,3)Fuc-T) which catalyzed the prototypical reaction: Galbeta-1,4GlcNAcR+GDP-fucose=>Galbeta-1,4GlcNAc-R 1-alpha,3 Fuc The human genome encodes several distinct alpha(1,3)Fuc-Ts as determined by biochemical studies. Each enzyme can react differentially with structurally distinct oligosaccharide precursors. DNA fragments for four human fucosyltransferases have been cloned. these enzymes have shared and distinct primary structures as well as shared and dictate their different catalytic activities. This family of glycosyltransferases is unique in that no other family of glycosyltransferases exhibit a similar dichotomy between structure and function. We propose to define the structural elements within these enzymes that dictate catalytic activity towards acceptor substrates and thus participate in the regulation the expression of distinct alpha(1,3)fucosylated oligosaccharides. This will be accomplished by mutation analysis of the cloned human fucosyltransferases. The minimal in vitro catalytic domain of an enzyme will be determined and correlated with in vivo activity. Additionally, we will define the primary sequence determinants within alpha(1,3)fucosyltransferases that modulate acceptor substrate specificity. Mutation of the DNA and expression of these fragments will be accomplished by previously described methods. The research proposal represents the Phase I research to be conducted during a Physician Scientist Award and will be accompanied by graduate course work. An advisory committee will oversee the progress of the applicant.